+ + = H
1
H NMR Interpretation:
A New Tool for Students
John V. McClusky
Texas Lutheran University
Texas Lutheran University
Why Teach NMR Interpretation?
• Necessary for molecular identification
• Important for teaching problem solving skills
– Complex and abstract
– Must concentrate on details and big picture
– “You guess, you loose”
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The Process
• Students must use
– Integration
• Number of hydrogens making the peak
– Multiplicity
• Number of adjacent hydrogens
– Chemical shift
• Functional groups
• Determine the molecular structure
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C
13
H
16
O
3
The Problem
© Sigm a-Aldrich Co. ALL RIGHTS RESERVED
300 MHz ¹H NMR
11 10 9 8 7 6 5 4
Doesn’t look like
O
O
H
3
C
H O
3 2 1
Texas Lutheran University
Typical Student Errors
• Ignore integration, multiplicity, or chemical shift
• Interpret multiplicity incorrectly
– n+1, n, or n-1?
– Switch integration and multiplicity
• Force spectrum to “match” preconceived molecule
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NMR Mosaic Goals
• Make NMR Interpretation more concrete
• Reinforce need to use all data
– Chemical shift
– Multiplicity
– Integration
• Visualize relationship between multiplicity and connectivity
• Retain all problem-solving aspects
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NMR Mosaic
Spectral peaks
Molecular fragments
Molecule fit
Finished mismatch
Revise --
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Strengths of the NMR Mosaic
• Requires use of integration, chemical shift, and multiplicity
• Accentuates interpretation errors
• Eases interpretation of complex multiplets
• Illustrates relationship between connectivity and multiplicity
Helps students understand and visualize NMR interpretation
Texas Lutheran University
Mosaic Pieces
Peak is from Splitting indicates Chemical shift Final mosaic piece a CH
2 adjacent CH
3 indicates adjacent functional group
H
|
─C─
|
H
+
CH
3
+ =
H
|
─C─
|
H
Students add static clings to generic pieces to produce a custom piece encoding connectivity and functionality
Texas Lutheran University
3.5
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
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1.2
1.1
1.0
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0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
3.5
H
|
─C─
|
H
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
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1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
3.5
CH
2
H
|
─C─
|
H
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
3.5
CH
2
H
|
─C─
|
H
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
CH
2
H
|
─C─
|
H
3.5
X-
Example: C
3
H
7
Cl
3.0
300 MHz ¹H NMR
In C DC l 3
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
CH
2
H
|
─C─
|
H
3.5
X-
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.0
CH
3
H
|
─C─
|
H
CH
2
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
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1.2
1.1
1.0
0.9
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0.7
0.6
0.5
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0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
CH
2
H
|
─C─
|
H
3.5
X-
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
H
|
H─C─
|
H
CH
2
CH
3
H
|
─C─
|
H
CH
2
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
3.5
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
H
|
H─C─
|
H
CH
2
CH
3
H
|
─C─
|
H
CH
2
CH
2
H
|
─C─
|
H
1-chloropropane
X-
3.0
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
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1.1
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0.7
0.6
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0.3
0.2
0.1
0.0
-0.1
1.0
Texas Lutheran University
NMR Mosaic Simplifies
Interpretation of Complex Multiplets
• Adjoining pieces specify connectivity
• Interpretation is no longer “impossible”
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Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3
X-
CH
2
H
|
─C─
|
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3
X-
CH
2
H
|
─C─
|
H
|
─C─
|
H
Undetermined
Splitting
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3 H
|
H─C─
|
H
CH
X-
CH
2
H
|
─C─
|
H
|
─C─
|
H
Undetermined
Splitting
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3 H
|
H─C─
|
H
CH
X-
CH
2
H
|
─C─
|
H
|
─C─
|
H
Undetermined
Splitting
H
|
H─C─
|
H
CH
2
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3
H
|
H─C─
|
H
CH
2
CH
2
H
|
─C─
|
X-
H
|
─C─
|
H
Undetermined
Splitting
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
Example: C
4
H
9
Cl
300 MHz ¹H NMR
In CDCl3
2-chlorobutane
H
|
H─C─
|
H
CH
2
CH
3
H
|
─C─
|
H
CH
CH
2
H
|
─C─
|
X-
5.0
4.5
4.0
3.5
3.0
2.5
2.0
© Sigma-Aldrich Co.
ALL RIGHTS RESERVED
1.5
1.0
0.5
Texas Lutheran University
1.00
0.75
0.50
0.25
0.00
NMR Mosaic Helps Students
Catch Mistakes
• Mosaic pieces no longer match
• Focus students on incorrectly interpreted peaks
Texas Lutheran University
C
3
H
7
Cl
X-
| | | |
| | | |
Example: C
3
H
7
Cl
3 0 0 M H z ¹ H N M R
I n C D C l 3
| | |
H
H─C─
| | |
| |
| |
Incorrect piece as an example
3 . 5 3 . 0 2 . 5 2 . 0
© S i g m a - A l d r i c h C o .
A L L R I G H T S R E S E R V E D
1 . 5 1 . 0
Texas Lutheran University
1 . 2
1 . 1
1 . 0
0 . 9
0 . 8
0 . 7
0 . 6
0 . 5
0 . 4
0 . 3
0 . 2
0 . 1
0 . 0
- 0 . 1
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
3.5
H
|
H─C─
|
H
3.0
CH
2
CH
3
H
|
─C─
|
H
CH
3
CH
2
H
|
─C─
|
H
Incorrect Match
↑
X-
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.0
Texas Lutheran University
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
3.5
Example: C
3
H
7
Cl
300 MHz ¹H NMR
In C DC l 3
H
|
H─C─
|
H
3.0
CH
2
CH
3
H
|
─C─
|
H
CH
2
CH
2
H
|
─C─
|
H
Corrected Piece
Matches
X-
2.5
2.0
© Si g m a -Al d ri c h C o .
AL L R IGHT S R E SE R VE D
1.5
1.0
Texas Lutheran University
1.2
1.1
1.0
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0.4
0.3
0.2
0.1
0.0
-0.1
Computer Version
• Same basic format as “hardware” version
• Extensive help section
• Over 50 problems, many including Infrared,
13 C NMR, and reaction sequences
• Student answers to problems are checked for correctness
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Main Program Work Area
Texas Lutheran University
Texas Lutheran University
Student Experiences
• Students found the NMR Mosaic a great aid in NMR
Interpretation
• Much higher percentage of students successfully solved problems
• Allows much more realistic problems on exams
• Better students weaned themselves off NMR Mosaic
• Students had a much stronger understanding of NMR interpretation
Texas Lutheran University
NMR Mosaic: Key Features
• Requires use of Integration, Multiplicity, and
Chemical Shift
• Accentuates students’ interpretation errors
• Eases interpretation of complex multiplets
• Reinforces relationship between multiplicity and connectivity
• Can be used with thousands of spectra
EMPHASIZES UNDERSTANDING AND
PROBLEM SOLVING SKILLS
Texas Lutheran University
Acknowledgement
Texas Lutheran University
www.tlu.edu/nmr
Texas Lutheran University
